Host Fidelity Research Articles

Expression differences in Aphidius ervi (Hymenoptera: Braconidae) females reared on different aphid host species.

The molecular mechanisms that allow generalist parasitoids to exploit many, often very distinct hosts are practically unknown. The wasp Aphidius ervi, a generalist koinobiont parasitoid of aphids, was introduced from Europe into Chile in the late 1970s to control agriculturally important aphid species. A recent study showed significant differences in host preference and host acceptance (infectivity) depending on the host A. ervi were reared on. In contrast, no genetic differentiation between A. ervi populations parasitizing different aphid species and aphids of the same species reared on different host plants was found in Chile. Additionally, the same study did not find any fitness effects in A. ervi if offspring were reared on a different host as their mothers. Here, we determined the effect of aphid host species (Sitobion avenae versus Acyrthosiphon pisum reared on two different host plants alfalfa and pea) on the transcriptome of adult A. ervi females. We found a large number of differentially expressed genes (between host species: head: 2,765; body: 1,216; within the same aphid host species reared on different host plants: alfalfa versus pea: head 593; body 222). As expected, the transcriptomes from parasitoids reared on the same host species (pea aphid) but originating from different host plants (pea versus alfalfa) were more similar to each other than the transcriptomes of parasitoids reared on a different aphid host and host plant (head: 648 and 1,524 transcripts; body: 566 and 428 transcripts). We found several differentially expressed odorant binding proteins and olfactory receptor proteins in particular, when we compared parasitoids from different host species. Additionally, we found differentially expressed genes involved in neuronal growth and development as well as signaling pathways. These results point towards a significant rewiring of the transcriptome of A. ervi depending on aphid-plant complex where parasitoids develop, even if different biotypes of a certain aphid host species (A. pisum) are reared on the same host plant. This difference seems to persist even after the different wasp populations were reared on the same aphid host in the laboratory for more than 50 generations. This indicates that either the imprinting process is very persistent or there is enough genetic/allelic variation between A. ervi populations. The role of distinct molecular mechanisms is discussed in terms of the formation of host fidelity.

Ecological coevolution of parasitoid, Acerophagus papayae noyes and Schauff on papaya mealybug, Paracoccus marginatus Williams and granara de Willink

The adaptive plasticity of parasitoid Acerophagus papayae noyes and Schauff on different host plants using the handling time, recognition time and survival probability of parasitoid via the infestivity of parasitoids using the reciprocal experiment is demonstrated to prove the existence of co-evolutionary arms race between parasitoids and insect pest. Papaya had significantly lower handling time and recognition time of 20.4 seconds and 4.8 seconds respectively. tapioca had higher handling time and recognition time of 38.8 seconds and 8.8 sec respectively. the infestivity of A. papayae shows host preferences mediated through host fidelity of some populations, demonstrated by significant differences in infectivity across the different hosts studied. This could be used to increase the effectiveness of biological control programme.

English

Abstract We analyzed historical data from 1961-1965 for species occurrences of branchiobdellidans and their crayfish hosts throughout the Mountain Lake Region of southwestern Virginia, USA to quantify geographic variability in species composition and identify patterns in host and symbiont diversity. We collected contemporary census data of branchiobdellidan assemblages from the same region in 2011-2014 for intra-annual variation in symbiont abundance and species composition. We compared historical and contemporary records to assess the stability of geographic patterns in symbiont diversity over decadal timescales. Branchiobdellidan assemblages followed a hump-shaped relationship with Strahler stream order. Much of the geographic variation in symbiont species composition was explained by host species composition, despite low host fidelity in branchiobdellidans. There were strong seasonal cycles in branchiobdellidan abundance and species composition. A comparison of historical and contemporary records revealed little change in species distributions over 50 years. Thus, branchiobdellidan species composition changes predictably along habitat gradients, tracks variation in host composition, is repeatable across decadal timescales, and follow strong cyclic seasonal changes in total and relative abundances. These results suggest that complex but deterministic ecological processes drive symbiont population dynamics at multiple spatial and temporal scales.

Host selection and preferences of coral symbiotic crab Tetralia rubridactyla

Coral symbiotic crabs provide considerable benefits to their host corals. A comprehensive understanding of the association between these crabs and their hosts could help clarify the relationship, interaction, and importance of symbionts with coral reefs as hosts. In this study, the coral symbiotic crab Tetralia rubridactyla was test for host preference and fidelity. Five oceanic objects were provided to the crabs: common host corals (Acropora hyacinthus and A. digitifera), uncommon host corals (Pocillopora damicornis and Stylophora pistillata), and dead coral skeletons. The crabs were collected from the 2 source host corals A. hyacinthus and A. digitifera and subjected to an experiment comprising 7 treatments. Each treatment included 2 stages of no-choice and choice conditions to estimate the expected selection frequencies. The results revealed that the crabs chose any available object under the no-choice condition, and exhibited various preferences under the choice condition. Moreover, T. rubridactyla exhibited significantly higher frequencies to inhabit Acropora corals (p<0.01, χ2 test), than dead coral skeletons and uncommon host corals. In all the treatments, the preferences of the crabs from the 2 source hosts were similar. Present results demonstrated T. rubridactyla host selection conditioning as follows: (1) Under the no-choice condition, inhabit any choice object for shelter; (2) under the choice condition, if without a common host, randomly inhabit any uncommon choice object as a host; and (3) under the choice condition, if a common host is available, selecting the common host is the first priority because it could provide food and space. This study revealed that T. rubridactyla express neither fidelity nor preference between A. hyacinthus and A. digitifera. Thus, these results also suggested that the distribution of T. rubridactyla on Acropora corals in the reef is affected by an abundance of corals rather than the preferences of coral species.

Loss of host fidelity in highly inbred populations of the parasitoid wasp Aphidius ervi (Hymenoptera: Braconidae)

Inbreeding frequently reduces the fitness of organisms, but little is known about how this phenomenon can affect the biological control. Host fidelity provides an adaptive advantage to aphid parasitoids, allowing females to find their aphid host more quickly in heterogeneous environments. This trait is mediated by the learning of signals, mainly chemical cues emitted from the host in which parasitoids developed (natal). This article is aimed at studying whether host fidelity can be altered after many generations of inbreeding reproduction in caged laboratory populations, for which host preference and fitness parameters were measured in the parasitoid wasp Aphidius ervi. Also, the effect of the natal/non-natal hosts was studied, using parasitoids originated from the pea aphid (Acyrthosiphon pisum) and the grain aphid (Sitobion avenae). We observed a loss of host fidelity in the studied A. ervi populations, irrespective of their natal aphid host, which contrasts with previous reports showing preference for natal hosts in outbred laboratory populations. The loss of host fidelity is discussed in terms of the origin of populations; the sex ratio was strongly biased toward males and long-time maintenance under laboratory conditions. Our results highlight the need for controlling the genetic diversity of caged parasitoids before they are released into fields, as a long period of inbreeding could negatively affect the biological control.

Population distribution, host-switching, and chemical sensing in the symbiotic shrimp Lysmata pederseni: implications for its mating system in a changing reef seascape

Lysmata pederseni, a protandric simultaneously hermaphroditic shrimp that inhabits the tube sponge Callyspongia vaginalis, is monogamous in the central and southeastern Caribbean Sea. We tested the null hypothesis of monogamy in a northern Caribbean population. In the Florida Keys, shrimps did not inhabit host individuals in pairs with a frequency greater than expected by chance alone. Hermaphrodites inhabited sponges solitarily and often brooded embryos. Hermaphrodites do not store sperm and need to be inseminated shortly after molting to fertilize a new batch of eggs. Thus, males and/or other hermaphrodites are likely switching among host individuals in search of sexual partners. Field experiments demonstrated low shrimp host fidelity. Host residence time was ~2 times shorter for males than for hermaphrodites. We inferred a polygynandrous mating system in L. pederseni from the Florida Keys, with male-role and young hermaphrodites often moving among sponges in search of older, more sedentary, female-role hermaphrodites. We expected shrimps to use water-borne chemical cues originating from conspecifics or sponges to locate sexual partners. Experiments demonstrated that shrimps were attracted to water-borne cues originating from sponges but not conspecifics. We have described the mating system of a reef-associated shrimp in a fast-pace shifting seascape increasingly dominated by sponges and vanishing stony corals. In the central and southeastern Caribbean Sea, with greater coral cover and lower sponge abundance than in the Florida Keys, the same species is monogamous. Whether or not similar shifts in the social organization of other coral reef-dwelling marine organisms are occurring due to contemporary changes in seascapes is a relevant topic that deserves further attention.

Determinants of host feeding success by Anopheles farauti.

BackgroundThe proportion of blood meals that mosquitoes take from a host species is a function of the interplay of extrinsic (abundance and location of potential hosts) and intrinsic (innate preference) factors. A mark-release-recapture experiment addressed whether host preference in a population of Anopheles farauti was uniform or if there were anthropophilic and zoophilic subpopulations. The corresponding fitness associated with selecting different hosts for blood meals was compared by measuring fecundity.MethodsThe attractiveness of humans for blood meals by An. farauti in the Solomon Islands was compared to pigs using tent traps. Host fidelity was assessed by mark-release-recapture experiments in which different colour dusts were linked to the host to which the mosquito was first attracted. Outdoor resting An. farauti were captured on barrier screens and the human blood index (HBI) as well as the feeding index were calculated. The fecundity of individual An. farauti after feeding on either humans or pigs was assessed from blood-fed mosquitoes held in individual oviposition chambers.ResultsAnopheles farauti were more attracted to humans than pigs at a ratio of 1.31:1.00. The mark-release-recapture experiment found evidence for An. farauti being a single population regarding host preference. The HBI of outdoor resting An. farauti was 0.93 and the feeding index was 1.29. Anopheles farauti that fed on a human host laid more eggs but had a longer oviposition time compared to An. farauti that had blood fed on a pig.ConclusionsOne of the strongest drivers for host species preference was the relative abundance of the different host species. Here, An. farauti have a slight preference for humans over pigs as blood meal sources. However, the limited availability of alternative hosts relative to humans in the Solomon Islands ensures a very high proportion of blood meals are obtained from humans, and thus, the transmission potential of malaria by An. farauti is high.Electronic supplementary materialThe online version of this article (doi:10.1186/s12936-016-1168-y) contains supplementary material, which is available to authorized users.

Attraction, Feeding Preference, and Performance of Spodoptera frugiperda Larvae (Lepidoptera: Noctuidae) Reared on Two Varieties of Maize.

The fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), is an economically important pest of maize and other crops in the Americas. Studies suggest that modern varieties of maize lost some of their natural defense mechanisms against herbivores during domestication and agricultural selection. In the present study, we evaluated the attraction, feeding preference (host fidelity and consumption rate), and performance of S. frugiperda larvae reared on hybrid (Pioneer P4063W) and landrace (Tuxpeño) varieties of maize. We also evaluated the damage caused by S. frugiperda to Pioneer and Tuxpeño maize plants in the field. We found that fifth-instar larvae were more attracted to Pioneer plants than to Tuxpeño plants in a Y-tube olfactometer. Additionally, the fall armyworm larvae showed more fidelity to Pioneer leaves than to Tuxpeño leaves. However, the larval consumption rate was similar for both types of maize plants. The life cycle of S. frugiperda was significantly longer when the larvae were reared on Tuxpeño leaves than on Pioneer leaves. In the field, the Pioneer variety was infested with more S. frugiperda larvae than the Tuxpeño variety. Thus, our results provide evidence that modern varieties of maize may have lost some of their defensive traits during selective breeding.

Effects of Female fruit-marking Pheromones on Oviposition, Mating, and Male Behavior in the Neotropical Species Rhagoletis conversa Bréthes and Rhagoletis brncici Frías (Diptera: Tephritidae).

Sex pheromones produced by females of Rhagoletis conversa Bréthes and Rhagoletis brncici Frías are deposited on the surface of fruits after the eggs are laid. These pheromones repel other females, preventing repeated oviposition on the same fruit. They also attract males, thus assisting mating. Observations were made on wild populations, and cross-species behavioral tests were performed on males. The pheromone released by females was significantly more attractive for males of the same species. The two species showed remarkable differences in mating behavior, in the duration of oviposition, and in the number of circuits made around the fruit after eggs were laid. A morphological analysis of flies collected from their respective host plants indicated great host fidelity and the reproductive isolation of the two species. Possibly, the specific male-arresting effect of this pheromone was important for the sympatric speciation and evolution of these sibling species.

Evidence of niche conservatism and host fidelity in the polar shrimp Lebbeus kiae n. sp. (Decapoda: Caridea: Thoridae) from the Ross Sea, Antarctica

We report a remarkable case of ‘bipolarism’, where two different polar species, namely Lebbeus polaris in the northern hemisphere and Lebbeus kiae n. sp., here described from the Southern Ocean, have been found to share similar ecologies. Despite the great geographical distance between the two species, both show high host fidelity in associations with two congeneric sea anemones: Bolocera tuediae and Bolocera kerguelensis, respectively. A close molecular phylogenetic relationship between the two Lebbeus species is indicated by COI data, which clearly show them as sister clades with respect to other congeners as well as a plurality of other Antarctic species. This is the first reported case of a defensive association in the Southern Ocean involving shrimps and sea anemones. The distribution of the new species, limited to seamount systems off the Ross Sea, may be the result of a specific colonisation/speciation event in the past, although more molecular data are needed to unravel the phylogenetic relationships within the genus Lebbeus. Despite this uncertainty, the persistence of ecological traits, i.e., the defensive association with sea anemones, indicates the presence of niche conservatism in this clade of shrimps.

Does sex-biased dispersal account for the lack of geographic and host-associated differentiation in introduced populations of an aphid parasitoid?

Host recognition and use in female parasitoids strongly relies on host fidelity, a plastic behavior which can significantly restrict the host preferences of parasitoids, thus reducing the gene flow between parasitoid populations attacking different insect hosts. However, the effect of migrant males on the genetic differentiation of populations has been frequently ignored in parasitoids, despite its known impact on gene flow between populations. Hence, we studied the extent of gene flow mediated by female and male parasitoids by assessing sibship relationships among parasitoids within and between populations, and its impact on geographic and host-associated differentiation in the aphid parasitoid Aphidius ervi. We report evidences of a high gene flow among parasitoid populations on different aphid hosts and geographic locations. The high gene flow among parasitoid populations was found to be largely male mediated, suggested by significant differences in the distribution of full-sib and paternal half-sib dyads of parasitoid populations.

Host fidelity over geologic time: restricted use of oaks by oak gallwasps

AbstractOaks and their associated gallwasps are often cited as a classic example of coevolution in a plant-insect system. Therefore, it is expected that these gallwasps should demonstrate a high degree of host fidelity over their evolutionary history. To test this, we studied 25 fossil floras from the Oligocene through Pliocene of the western United States. Galls were found on the leaves ofQuercus simulata-type Knowlton, 1898 andQ. pollardiana-type (Knowlton) Axelrod, 1940, and match previously reported galls of the form genusAntronoidesWaggoner and Poteet, 1996. These fossil leaf-galls are similar to those made on oaks by modern Cynipini wasps, and were restricted to two oak species. Galls are present on these oaks in western floras for a span of 30 million years, indicative of remarkable host fidelity through time. The distribution of galled leaves from across the western United States indicates that the radiation of this group of gallwasps occurred more or less simultaneously across a wide geographic area.

Seasonal alterations in host range and fidelity in the polyphagous mirid bug, Apolygus lucorum (Heteroptera: Miridae).

In herbivorous insects, host plant switching is commonly observed and plays an important role in their annual life cycle. However, much remains to be learned about seasonal host switching of various pestiferous arthropods under natural conditions. From 2006 until 2012, we assessed Apolygus lucorum (Meyer-Dür) host plant use in successive spring, summer and winter seasons at one single location (Langfang, China). Data were used to quantify changes in host plant breadth and host fidelity between seasons. Host fidelity of A. lucorum differed between seasons, with 87.9% of spring hosts also used in the summer and 36.1% of summer hosts used in winter. In contrast, as little as 25.6% host plant species were shared between winter and spring. Annual herbaceous plants are most often used for overwintering, while perennial woody plants are relatively important for initial population build-up in the spring. Our study contributes to an improved understanding of evolutionary interactions between A. lucorum and its host plants and lays the groundwork for the design of population management strategies for this important pest in myriad crops.

Genomics and host specialization of honey bee and bumble bee gut symbionts.

Gilliamella apicola and Snodgrassella alvi are dominant members of the honey bee (Apis spp.) and bumble bee (Bombus spp.) gut microbiota. We generated complete genomes of the type strains G. apicola wkB1(T) and S. alvi wkB2(T) (isolated from Apis), as well as draft genomes for four other strains from Bombus. G. apicola and S. alvi were found to occupy very different metabolic niches: The former is a saccharolytic fermenter, whereas the latter is an oxidizer of carboxylic acids. Together, they may form a syntrophic network for partitioning of metabolic resources. Both species possessed numerous genes [type 6 secretion systems, repeats in toxin (RTX) toxins, RHS proteins, adhesins, and type IV pili] that likely mediate cell-cell interactions and gut colonization. Variation in these genes could account for the host fidelity of strains observed in previous phylogenetic studies. Here, we also show the first experimental evidence, to our knowledge, for this specificity in vivo: Strains of S. alvi were able to colonize their native bee host but not bees of another genus. Consistent with specific, long-term host association, comparative genomic analysis revealed a deep divergence and little or no gene flow between Apis and Bombus gut symbionts. However, within a host type (Apis or Bombus), we detected signs of horizontal gene transfer between G. apicola and S. alvi, demonstrating the importance of the broader gut community in shaping the evolution of any one member. Our results show that host specificity is likely driven by multiple factors, including direct host-microbe interactions, microbe-microbe interactions, and social transmission.

Host Specificity And Co-Speciation In Avian Haemosporidia In The Western Cape, South Africa

Host and pathogen ecology are often closely linked, with evolutionary processes often leading to the development of host specificity traits in some pathogens. Host specificity may range from ‘generalist’, where pathogens infect any available competent host; to ‘specialist’, where pathogens repeatedly infect specific host species or families. Avian malaria ecology in the region remains largely unexplored, despite the presence of vulnerable endemic avian species. We analysed the expression of host specificity in avian haemosporidia, by applying a previously developed host specificity index to lineages isolated from wetland passerines in the Western Cape, South Africa. Parasite lineages were isolated using PCR and identified when possible using matching lineages deposited in GenBank and in MalAvi. Parasitic clades were constructed from phylogenetic trees consisting of Plasmodium and Haemoproteus lineages. Isolated lineages matched some strains of Plasmodium relictum, P. elongatum, Haemoproteus sylvae and H. lanii. Plasmodium lineages infected a wide range of hosts from several avian families in a generalist pattern of infection. Plasmodium spp. also exhibited an infection trend according to host abundance rather than host species. By contrast, Haemoproteus lineages were typically restricted to one or two host species or families, and displayed higher host fidelity than Plasmodium spp. The findings confirm that a range of host specificity traits are exhibited by avian haemosporidia in the region. The traits show the potential to not only impact infection prevalence within specific host species, but also to affect patterns of infection at the community level.

Host-use patterns and factors influencing the choice between anemone and urchin hosts by a caridean shrimp

Small marine decapods often associate with other invertebrates in order to gain protection from predators. However, the factors that influence host choice by symbionts, such as shrimps, are poorly understood but may have important implications for the distribution and abundance of these mesoconsumers. In Hong Kong, the rhynchocinetid shrimp Rhynchocinetes brucei uses two alternative hosts: an urchin (Diadema setosum) and an anemone (Entacmaea quadricolor). We examined the association between R. brucei and its anemone and urchin hosts in the field and laboratory, investigating host choice and host fidelity. Underwater surveys on shallow rocky reefs in Hong Kong revealed that shrimps were rarely found outside refuges, such as crevices and holes, unless they were associated with anemones and urchins. Shrimps were more frequently associated with urchins than with anemones, although anemones were more abundant within the survey area. Host-choice experiments in the laboratory confirmed that, when given a choice, shrimps avoided open areas and associated with anemones, urchins or artificial refuges. Shrimps overwhelmingly chose urchins over artificial refuges, but did not show any clear preference for anemones over refuges. When offered a choice, shrimps displayed fidelity for their original host species (i.e. the host with which they were associated when collected from the field), suggesting that they imprinted upon the host. Host-imprinting may allow symbionts to efficiently relocate their original host species after separation (e.g. following nocturnal foraging trips) thereby, perhaps, reducing the risk of predation. However, host preference by R. brucei was facultative because shrimps would associate with an unfamiliar host when their original host was unavailable. This flexibility may allow shrimps to respond to local variability in host abundance.

Divergent host plant preference causes assortative mating between sympatric host races of the ladybird beetle,Henosepilachna diekei

Divergent host preference (i.e. host fidelity) plays a significant role in the speciation process in phytophagous insects. However, how and to what extent this divergence reduces gene flow between populations has rarely been measured. Here, we estimated the intensity of assortative mating caused solely by host fidelity in two host races of the phytophagous ladybird beetle Henosepilachna diekei, specialized on Mikania micrantha (Asteraceae) and Leucas lavandulifolia (Lamiaceae) in West Java, Indonesia. These host races mated randomly in the absence of host plants under laboratory conditions, but demonstrated nearly complete assortative mating in field cages with the two host plants, by spending almost all of their time on their respective host plants. The frequency of assortative mating in the field cages was not affected drastically by host plant patch structure. These results suggest that fidelity to the different host plants yields directly almost complete reproductive isolation between the host races by limiting the habitat on the respective host plant. In addition, the high host fidelity also ensures female oviposition on the original host plant. As larvae cannot survive on non-host plants, a positive association between female oviposition preference and larval performance on the host plant on which the beetles are specialized will further facilitate the evolution of host fidelity. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 606–614.

Host acceptance behavior of the parasitoid Aphelinus mali and its aphid-host Eriosoma lanigerum on two Rosaceae plant species

The presence of a natural enemy in a habitat refuge is no guarantee of emigration by these into crop fields, when pest population outbreaks occur. Parasitoids from a refuge may not prefer foraging on the pest crop, exhibiting host fidelity, and therefore not constituting a source of natural enemies for improving biological control. An effective refuge must not only be a suitable sink for natural enemies, providing an acceptable host when these are not present in the crop, but it must also be a suitable source of parasitoids that readily accept the aphid-host on the crop. Therefore, crop-originated parasitoids would have to accept pests from the refuge as hosts to lay eggs in, and refuge-originated parasitoids would have to accept and lay eggs in pests from the crop. We here study the host fidelity of populations of Eriosoma lanigerum originating from two host plants (firethorn and apple) through reciprocal transfer experiments. Thereafter, the host fidelity of parasitoids from populations in the two host plants (firethorn and apple) was assessed. Reciprocal transfer experiments of parasitoids did not show an association between apple-originated parasitoids and their preference for any of the aphid hosts. Conversely, parasitoids from firethorn exhibited a higher number of attacks and in less time when aphids from apple were offered, suggesting a preference for apple-originated aphids. If future field work confirms these findings, firethorn could become an important management tool for enhancing biological control of woolly apple aphid in apple orchards, without being a substantial source of aphids.

Ecological speciation in anemone‐associated snapping shrimps (Alpheus armatus species complex)

Divergent natural selection driven by competition for limited resources can promote speciation, even in the presence of gene flow. Reproductive isolation is more likely to result from divergent selection when the partitioned resource is closely linked to mating. Obligate symbiosis and host fidelity (mating on or near the host) can provide this link, creating ideal conditions for speciation in the absence of physical barriers to dispersal. Symbiotic organisms often experience competition for hosts, and host fidelity ensures that divergent selection for a specific host or host habitat can lead to speciation and strengthen pre-existing reproductive barriers. Here, we present evidence that diversification of a sympatric species complex occurred despite the potential for gene flow and that partitioning of host resources (both by species and by host habitat) has contributed to this diversification. Four species of snapping shrimps (Alpheus armatus, A.immaculatus, A.polystictus and A.roquensis) are distributed mainly sympatrically in the Caribbean, while the fifth species (A.rudolphi) is restricted to Brazil. All five species are obligate commensals of sea anemones with a high degree of fidelity and ecological specificity for host species and habitat. We analysed sequence data from 10 nuclear genes and the mitochondrial COI gene in 11-16 individuals from each of the Caribbean taxa and from the only available specimen of the Brazilian taxon. Phylogenetic analyses support morphology-based species assignments and a well-supported Caribbean clade. The Brazilian A.rudolphi is recovered as an outgroup to the Caribbean taxa. Isolation-migration coalescent analysis provides evidence for historical gene flow among sympatric sister species. Our data suggest that both selection for a novel host and selection for host microhabitat may have promoted diversification of this complex despite gene flow.

Biogeography and Host Fidelity of Bacterial Communities in Ircinia spp. from the Bahamas

Research on sponge microbial assemblages has revealed different trends in the geographic variability and specificity of bacterial symbionts. Here, we combined replicated terminal-restriction fragment length polymorphism (T-RFLP) and clone library analyses of 16S rRNA gene sequences to investigate the biogeographic and host-specific structure of bacterial communities in two congeneric and sympatric sponges: Ircinia strobilina, two color morphs of Ircinia felix and ambient seawater. Samples were collected from five islands of the Bahamas separated by 80 to 400 km. T-RFLP profiles revealed significant differences in bacterial community structure among sponge hosts and ambient bacterioplankton. Pairwise statistical comparisons of clone libraries confirmed the specificity of the bacterial assemblages to each host species and differentiated symbiont communities between color morphs of I. felix. Overall, differences in bacterial communities within each host species and morph were unrelated to location. Our results show a high degree of symbiont fidelity to host sponge across a spatial scale of up to 400 km, suggesting that host-specific rather than biogeographic factors play a primary role in structuring and maintaining sponge-bacteria relationships in Ircinia species from the Bahamas.